Two-stage oscillograph



1940. P. T. FARNSWORTH TWO-STAGE OSCILLOGRAFH Filed March 22-, 193'! kIN V EN TOR. PHIL o 7. Eve/vs WORTH Patented Oct. 1, 1940 UNITED STATESTWO-STAGE OSCILLOGRAPH Philo T. Farnsworth, Springfield Township,MontgomeryCounty, Pa., assignor, by mesneassignments, to FarnsworthTelevision & Radio 'Corporation, Dover, Del., a corporation of DelawareApplication March 22, 1937, Serial No. 132,323

1'7 Claims.

My invention relates to oscillographs, and particularly-to a two-stagecathode'ray oscillograph for television use, and embodies the broadprinciple of image amplification set forth in my prior 5 applicationentitled Electron image amplifier,

Serial No. 461,l10,filed June 14, 1930, now Patent No. 2,085,742,granted July 6, 1937.

Among the objects of my invention are: To provide a cathode rayoscillograph of greater sensitivity; to provide a more eificientoscillograph for television and other uses; to provide means fordeveloping'an amplified cathode ray beam within an oscillograph; toprovide a method of increasing the beam power within an os'cillographavailable for image production fora given value of primary beam'current;to provide means for producing a morebrilliant visual image from a givenprimary beam; and to provide an oscillograph wherein an electron beam isutilized toproduce an incandescent line image, and'said line image isutilized 'to produce an entire image or will be specifically pointed outin the de scription forming a part of this specification, but I do notlimit myself to the embodiment of the invention herein described, asvarious forms may be adopted within the scope of the claims.

My invention consists, briefly, in providing within an oscillograph tubean incandescible electrode of width equal to that of the desired pictureand height roughly equal to one picture element, across which each lineof the picture to be produced shall in turn be scanned, whereby theelectrode shall be incandesced ineach elementary length thereof to adegree, correspond ing to the light intensity of the correspondingpicture element: the. incandescent line image thus produced, consistingof thermionic electron and secondarily emitted electrons, is inturndirected upon a viewing or projecting screen, with successive lineimage's displaced from each other by a suitable deflecting field to forman entire image By making the first electrode of highly emissivematerial, the number of electrons producing each element of the entireimage may be increased without increasing the emission from the gun, anda more brilliant image may be therebyobtained'without increasing theaccelerating potentials or the size of the gun.

Referring to the drawing: Figure 1 is a schematic sectional view of anoscillograph employing my invention.

Figure 2 is a cross-sectional schematic view, 5 taken along line 2--2 ofFigure 1, showing the o1. H's-7.5)

structure of the intermediate electrode enlarged in proportion to the"remainder of the tube.

The brilliance of an image produced in a cathode ray oscillograph isdependent upon a number of factors, among which are the average number 5of electrons in the cathode ray beam and the construction of the screenupon which the image is produced. In the Farnsworth application entitledIncandescent light source, Serial No. 67,889, filed March 9, 1936, nowmatured into 10 U. S. Patent No. 2,089,054, issued August 3, 1937, itwas pointed out that the essen'tialrequirements for brilliance in anincandescible screen are that the screen mass be small and that heatlosses shall be by radiation rather than by conduction: is in thatapplication and in variousrelated cases, a type of-screen constructionbelieved to offer a satisfactory answer to the problem was described,

- and the type of screen utilized in this'oscillograph tron emission atlow energy loss, since the energy 30 utilized therein is confined to theregion of maximum emission per unit of power absorbed. This may betterbe understood by reference to the drawing, 'a'more detailed descriptionof which is as follows: I

In Figure 1 'I have shown a cathode ray tube embodying my invention. Along, evacuated, cy-' lindrical envelope I of glass or similarinsulating material is terminated at one end-by a reentrant stem 2, andat the opposite end by an enlarged o rounded head 4. An electron gun 5is supported at the end of envelope I near the-reentrant stem 2. In thefigure, I have represented this gun conventionally as composed of a'filamentary cathode 6 supported by leads land 9 sealed 5 through thepress I0 terminatingthe reentrant stem 2, an apertured control electrodeH supported by a lead l2 sealed through the press l0, and a gun-typeanode l4 carried by a supporting lead l5 sealed through the wall ofenvelope I. 50 However, any combination of anode, cathode and controlelectrode which will produce a modulated electron beam is deemed a fullequivalent ofthe gun 5, as shown. 1

When cathode 6 is heated by a battery l6 or equivalent source of energy,electrons are emitted therefrom and attracted toward anode H by apositive potential placed thereon by a battery 11, or an equivalentdirect current source, through lead IS. The number reaching said anodeis controlled in accord with a charge built up on the control electrodeII by a signal current applied thereto through an input lead 19,condenser 20, and supporting lead l2. The gun 5 thus directs asignal-modulated beam of electrons along-the axis of tube I in accordwith well known practice, the electrons being accelerated by a positivepotential produced by a battery 2| on an intermediate electron emittingelectrode 22, diametrically disposed in a horizontal plane acrossenvelope l, as more clearly indicated in Figure 2.

An electrostatic shield 24 covers the inner wall of envelope I from apoint near the gun 5 tea point slightly beyond electrode 22, althoughinsulated therefrom. By virtue of a connection 25 to the gun anode lead15, shield 24 is maintained at anode potential, and prevents, unwanteddisturbance of the electrons traveling from gun to screen. This shieldmay be a metal cylinder inserted in the envelope, or may beformed byevaporating a conducting coat on the wall; a metal sleeve disposed aboutthe exterior of envelope! would serve the same purpose. I n a a Themodulatedbeam is caused to traverse electrode 22 by the magnetic fieldset up by diametrally spaced coils 26 (indicated schematically as onecoil), connected to a sawtooth os cillator 21 tuned to the proper highscanning frequency, and the impact of the; beam upon electrode 22 heatsit to a; degree of incandescent varying along its length in accord withthe variable light intensity of the picture element in correspondingposition. A battery 29 may be used to heat electrode 22 to a dull redglow, in order that all the energy in thebeam may be utilized inproducing visible changes. 5 Otherwise, a considerable proportion ,ofthe beam energy would be wasted in heating the electrode toincandescence. If desired, this polarizing heat might be supplied bydirecting infra-red radiations upon the electrode 22 from a lamp, or anauxiliarygun might be provided, to direct an unmodulated stream-felectrons upon the said electrode.

The electrode 22, in its preferred form, is

formed by winding about 250 turns per inch of fine refractory wire, suchas tungsten, upon a mandrel having a diameter'of about .003 inch, andthen etching the coil in hot sodium nitrite until the wire diameter isreduced to .00025 inch. Itis supported by spot-welding the ends, undertension, to leads 23 and 28 sealedithrough the envelope i. This methodof forming acoil to be incandesced has been described in the pendingFarnsworth application entitled fIncandescent light source, Serial No.67,889, filed March 9, 1936, now matured into U. S. Patent No. 2,089,-054, issued August 3, 1937, and as there pointed out, the efliciency ishigh, due to the small mass to be heated and the high percentage of heatloss by radiation as opposed to conduction.

The electron line image thus produced, composed of secondarily emittedelectrons thrown out by impact of the beam, and thermionic emission dueto incandescence, is attracted along the tube toward a viewing orprojecting screen 30, which is preferably formed of a numberof coilssimilar to electrode 22, held parallelly in aplane in ac-f cordance withthe teaching of the Farnsworth application, cited supra. Various otheror the 'trode 22.

applicant's screens may be used alternatively therewith, and are deemedfull equivalents thereof.

The electronic line image from the intermediate electrode 22 isaccelerated toward the projecting or picture screen 30 by a highpositive potential from a battery 3| or equivalent source of directcurrent. The electron image components tend to spread out, due to themutual repulsion oftheir negative charges, but are prevented from doingso by the field set up about solenoid 32 when energized by a battery34..

These magnetic focusing means cause the electrons to travel in meanrectilinear paths from electrode 22 to screen 30, and thus maintain thesame relative intensity at screen 30 as at elec- Successive line imagesare deflected by the field set up in diametrally placed coils 35,indicated schematically as a single coil, by sawtooth oscillator 36operating at low scanning frequency.

Itwill be noted fthat the high and low frequency scanning coils 26 and35 are shown in Figure 1 as occupying nearly the, same angular positionabout the axis of envelope I, although their effect is exerted normal toeach other. The reason for this position is found in the influence ofsolenoid 3'2. Thefield due to coil 2 traverses the beam horizontallyalong electrode 22, while the resultant field, due to coil 35' andsolenoid 32, produces a vertical defiectionof the line image. The fieldof solenoid .32 may, de-' pending on thestrength oi thecurrent frombattery 34 and the spacing of the parts, influence the field produced bycoils 26.x Theresultant field, which will be rotated about the axis ofthe tube to a degree dependent on the strength or the solenoid fieldcomponent, would cause a deflection of the beam Iromgun along a diameterat an angle to the horizontah, In practice, this is corrected byrotating coils 26 aboutthe tube until horizontal deflection is againsecured; similarly, coils 35 may be rotated until the resultant fieldproduces a vertical deflection of the line image. These adjustments maybe checked visually by maintaining a square image on screen 30.

Screen 30 may-be polarized by means, not

shown in the drawing, similar tothose used" with electrode 22, and theentireelectronic impact utilized to. produce'an intensely incandescentimage of the televised pictured or scene.

The end 4 of the tube has been made large to provide ample heatradiating surface.

The incandescent image may be projected through a suitable focusing lenssystem 31,

shown schematically, upon a suitable viewing.

screen, not shown, or for direct observation.

In short, by forming upon an intermediate electrode successiveincandescent line images,

and utilizing these intense line images to pro-:

duce the'entire image, I am, able to secure a much more intense imagewithout increasing the beam power or raising the accelerating potential.on the projecting screen, and am able to eiil'ect amazes screen capableof emitting light when bombarded j with electrons from said linearelectrode and positioned on the other side of said linear elec--*positively relative to said anode, and meansfor charging saidtwo-dimensional screen positively with relation to said linearelectrode.-

3. Apparatus in accordance with the recitation of claim 1, wherein thetwo-dimensional screen is a screen incandescible upon electron impacttherewith. c

4. Apparatus in accordance with claim 1,

refractory electron emitting wire of substantially .00025' inch wirediameter, said coil having approximately 250 turns per inch with a coildiam eter of substantially .003 inch. Y

5. A 'cathode ray oscillograph comprising an evacuated envelopehaving-therein a cathode, a control electrode and a gun type anode,cooperating, when energized as an electron gun, to produce a modulatedbeam of electrons of elemental cross section, an intermediate electronemitting electrode extending across said envelope, alined with said gunanode and having dimensions corresponding to one picture line, meanspositioned to move electrons from said beam linearly and cyclically overthe long dimension of said electron emitting electrode to produceheating thereof and consequent electron emission, a picture screencapable of producing light upon electron impact therewith positioned inthe path of electron emission from said electron emitting electrode, anda second scanning means positioned to move electrons emitted from saidelectron emitting electrode across said picture screen to produce animage on said picture screen corresponding to the modulations of themodulated beam.

6. A cathode ray oscillograph as recited in claim 5, having a magneticsolenoid surrounding the electron path between the intermediate screenand the second screen.

'7. A cathode ray oscillograph as recited in claim 5, wherein themodulations of the initial beam correspond to television signals,wherein the electron emission from the intermediate screen correspondsto a complete line of a television picture, and wherein the image on thesecond screen corresponds to the complete picture area.

8. A cathode ray oscillograph as recited in claim 5, wherein the firstscanning means is a high frequency movement, and wherein the secondscanning means accomplishes a low frequency scansion movement.

9. In combination, a screen whose surface emits light when bombardedwith electrons, a thermionic cathode providing a stream of electronsdirected at said screen, means for energizing said cathode to atemperature slightly less than that at which said cathode emitselectrons in substantial quantities, a source of picture signalmodulated electrons, means for bombarding said cathode with electronsfrom said source to raise the instantaneous temperature of said cathodein accordance with the modulation of electrons from said source, theelectrons thereupon-emitted by said cathode being modulated in iaccordance with'said-picture signals, and means for scanning said screenin a pre-determined pat-v tern of lines with the streamof electronsemitted by said cathode. to produce on said screen a visual image. 1' 11 Y 10. In combination, a screen whose surface emits light whenbombarded with electrons, an elongated cathodezproviding along itslengtha stream of electrons directed at said screen, means formodulating the stream of electrons flowing from said cathode to provideat successive in tervals, .of time electronic images of successive linesofa picture to be reproduced on said screen,

and means, for sweeping said stream of electron r} over said-screen inadirection transverse to the axis of said cathode.

11. In combination, a screen whose "incre mental surface areas emitlight when bombarded with electrons, a substantially linear cathodeproviding along its length a stream of electrons directed at saidscreen, means for modulating the stream of 'electronsemitted by saidcathode to provide at successive intervals of time electronic images ofsuccessive ones of a system of lines which together, form a picture onsaid. screen, and means forsweeping with substantially constant velocitysaid stream, of electrons over said screen in a direction transverse tothe axis ofv said cathode. I

12. The combination o'fa screen whose surface emits luminous energy whenbombarded with electrons, an elongated cathode providing along itslength a stream of electrons directed atv said screen, means for causingsaid electrons to bombard said screen, means for modulating the streamof electrons flowing from said cathode to provide at successiveintervals of time electronic images of successive ones of a system oflines which together form a picture on said screen, means for focusingsaid stream of electrons upon said screen as a line of finite length andoptimum breadth, and means for sweeping said stream of electrons oversaid screen in a direction at an angle to the axis of said cathode.

13. The combination, in a recording system, of a screen whoseincremental surface areas emit light when bombarded with electrons, anelongated thermionic cathode providing along its length a stream ofelectrons directed at said screen, means for energizing said cathode toa temperature slightly less than that at which said cathode emitselectrons in substantial quantities, means for increasing theinstantaneous temperature of incremental lengths of said cathode to atemperature at which said incremental lengths of said cathode emitelectrons in increased quantities, said last named means modulating thestream of electrons flowing from said cathode to provide at successiveintervals of time electronic images of successive ones of a pattern oflines which together form a picture on said screen, and means forsweeping said stream of electrons over said screen in a directiontransverse to the axis of said cathode.

14. In a recording system, the combination of I stream to provide atsuccessive intervals of time Q electronic images of successive ones of apattern of lines which together form a picture on said screen, and meansfor sweeping-said stream of electrons over said screen in a directiontransverse to the plane of said stream of electrons.

15. In combination, a screen whose surface emits light when bombardedwith electrons, an elongated cathode providing along its length a streamof electrons directed at said screen, a

second source of electrons,.meansifor bombarding said cathode along itslength with electrons from said'second named source, the electrons fromsaid second named-source being modulated through successiveintervalsoftime in accordance with'the light and shadow of successive ones of apattern of lines which together form a picture to be reproduced'on saidscreenyrneans responsive to the bombardment of said cathode ,byelectrons from said second named source for producing a modulation ofthe stream of electrons flowing from said cathode toward said screen toprovide at successive intervals of time electronic images of successiveones of said pattern of lines which together form a picture on saidscreen, and means for sweeping'said stream of electrons emitted by saidcathode over said screen in a direction transverse to the axis of saidcathode.

16. In combination, a screen whose surface emits light when bombardmentwith electrons, an elongated cathode providing along its length a streamof electrons directed at said screen, a source of electrons modulatedwith picture signals, means for periodicallysweeping said cathodealongits length with modulated electrons from said second named source,each such peri-J odical traversal of said cathode by said electronsefiecting themodulation of the stream of electrons emitted by saidcathodein accordance with the values of light, and shadow along thelength of a respective one of a system'of lines which form the pictureto be reproduced on said screen,

and means for sweeping said stream of electrons over said screen in adirection transverse to the axis of said cathode. I a

17-. The combination, in a recording system, .01 a screen whose surfaceemitslight when bombarded with electrons, a source of electronsmodulated with picture signals, an elongated thermionic cathodeproviding along its length a stream of electrons directed at saidscreen, means for energizing said cathode to a temperature slightly lessthan that at which said cathode emits electrons in substantialquantities, means for periodically sweeping said cathode along its.-length-with modulated electrons from said first electrons overvsaidscreen ina direction trans-,

verse to the'axis of said cathode. I

PHILO T. FARNSWORTH.

